Examples of writable optical recording media with which recording is carried out using light are write once optical discs for which recording can be carried out only once, and rewritable optical discs for which recording can be carried out a plurality of times by repeatedly erasing and writing; in recent years, there have been greater and greater advances in increasing recording capacity, this being by shortening the wavelength of the recording laser and using a lens having a high numerical aperture NA.
Taking the recording capacity per layer with a 12 cm diameter size as an example, with a digital versatile disc (DVD), which uses a laser of wavelength 635 to 660 nm and a objective lens having an numerical aperture NA of 0.60, a recording capacity of 4.7 GB has been achieved, and with a Blu-ray Disc, which uses a laser of wavelength 405 nm and a objective lens having an numerical aperture NA of 0.85, a recording capacity of 23 GB or more has been achieved.
A write once optical disc general has a substrate, and a writable information recording layer formed on the substrate; an organic dye material or a phase change material is used in the information recording layer.
A single-sided one-layer type writable optical recording medium is generally constituted from a substrate having an concavity-convexity pattern comprising grooves and lands, a rewritable information recording layer formed on the substrate, and a protective film bonded to the information recording layer via an adhesive layer. The rewritable information recording layer is generally constituted from a reflecting layer, a dielectric layer, a phase change layer and a dielectric layer.
Methods known for bonding the protective film and the information recording layer together include a method in which an ultraviolet curable resin is coated onto the protective film or the information recording layer, and then the protective film and the information recording layer are stuck together (Japanese Patent Application Laid-open No. 10-283683), and a method in which an acrylic adhesive layer (an adhesive sheet) having a release sheet is stuck onto the protective film or the information recording layer, the release sheet is peeled off, and the protective film and the information recording layer are stuck together via the exposed acrylic adhesive layer (Japanese Patent Application Laid-open No. 2000-67468).
Moreover, a single-sided two-layer type writable optical recording medium is generally produced by, for example, a method in which a first information recording layer (reflecting layer/dielectric layer/phase change layer/dielectric layer) is formed on a substrate having an concavity-convexity pattern, an ultraviolet curable resin is coated onto the first information recording layer, and then an concavity-convexity pattern is transferred onto the ultraviolet curable resin layer using a stamper, a second information recording layer (reflecting layer (translucent layer)/dielectric layer/phase change layer/dielectric layer) is further formed on the ultraviolet curing resin layer, and then a protective film is bonded onto the second information recording layer via an adhesive layer (as with the single-sided one-layer type) (Japanese Patent Application Laid-open No. 2000-36135).
However, with conventional writable optical recording media, there has been a problem that, if recording/erasure or reproduction of information is carried out repeatedly, then it becomes impossible to reproduce recorded information accurately. This problem has been particularly prominent in the case of using an acrylic adhesive when bonding on the protective film.